The Mundic Problem

Since the decline in use of natural stone at the beginning of the twentieth century most domestic and small commercial properties in Cornwall and South Devon have been built with concrete blocks or mass concrete. Until the mid-1950’s concrete blocks were often locally made, sometimes by individual builders, and shuttered concrete was mixed on site.

Before the second world war concrete products were rarely transported more than 20 km. Because concrete was made where it was needed and as transport was difficult and costly, aggregates were sought locally. Now all blocks are factory produced and mass concrete is supplied ready-mixed from facilities where manufacture is strictly controlled.

In many parts of Cornwall and South Devon ample supplies of cheap and often suitably graded aggregate were available as waste materials from the region’s metalliferous mining industry. The use of mining and, more particularly, ore processing wastes as aggregates, is central to the problem of accelerated concrete degradation in the region. It is widely called “the mundic block problem”.

Mundic is an old Cornish word for the common sulphide mineral pyrite. Accelerated deterioration is generally associated with the in situ oxidation of pyrite (and other sulphide minerals) in mine waste aggregates and sulphuric acid attack on the cement. Deterioration is occasionally so severe that concrete becomes structurally unsafe and some properties have had to be demolished.

In 1994 the Royal Institute of Chartered Surveyors (RICS) published guidelines for the testing of concrete block and shuttered mass concrete from properties built prior to the mid-1950's. This original guidance note has since been up-dated and amended. The testing regime so established has been designed to classify the concrete, primarily to satisfy lending institutions that a property is fit to mortgage on normal terms.